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Basic features of a clamp meter (Fluke 376 shown here).

What is a clamp meter?

A clamp meter is an electrical test tool that combines a basic digital multimeter with a current sensor.

Clamps measure current. Probes measure voltage. Having a hinged jaw integrated into an electrical meter allows technicians to clamp the jaws around a wire, cable or other conductor at any point in an electrical system, then measure current in that circuit without disconnecting/deenergizing it.

Beneath their plastic moldings, hard jaws consist of ferrite iron and are engineered to detect, concentrate and measure the magnetic field being generated by current as it flows through a conductor.

Alignment marks: To meet accuracy specifications, a conductor must be aligned with these marks.

Common input jack.

Volts/ohm input jack.

Input for flexible current probe.

Originally created as a single-purpose test tool, modern clamp meters offer more measurement functions, greater accuracy and in some cases specialized measurement features. Today’s clamp meters include most of the basic functions of a digital multimeter (DMM), such as the ability to measure voltage, continuity and resistance.

Clamp meters have become popular tools primarily for two reasons:

Safety. Clamp meters allow electricians to bypass the old-school method of cutting into a wire and inserting a meter’s test leads into the circuit to take an in-line current measurement. The jaws of a clamp meter do not need to touch a conductor during a measurement.

Convenience. During a measurement, it is not necessary to shut off the circuit carrying current—a big boost in efficiency.

Clamp meters are preferred for measuring high levels of current. DMMs cannot measure 10 A of current for more than 30 seconds without risking damage to the meter.

Clamp meters offer a minimum current range of 0 A to 100 A. Many models have a range up to 600 A. Others go up to 999 A or 1400 A, and some plug-in clamp accessories such as the iFlex® can measure as high as 2500 A.

Clamp meters are used on industrial equipment, industrial controls, residential/commercial/industrial electrical systems, and commercial/industrial HVAC. They are primarily used for: